Preparation, Reactions, and Stereochemistry of 4-Methyl-4-phosphatetracyclo2,8.03,6>octane 4-Oxide and Derivatives

Article abstract of DOI:10.1021/jo00028a022

The cis isomer 1b of the title compound was observed for the first time.It was prepared as a mixture with the previously reported trans isomer 1a.Reduction of the latter under sterically controlled conditions enabled selective formation of either the cis or trans tetracyclic phosphine 7.Although oxidation of the phosphine gave none of the expected phosphine oxide, stereoselective reactions with sulfur or selenium gave the cis and trans sulfides and selenides.Likewise, each phosphine isomer was transformed into several phosphonium salts by quaternization with methyl bromide, benzyl bromide, and p-nitro- and p-fluorobenzyl bromide.Stereochemical assignments for 1a and 1b were based on NMR lanthanide shift experiments.Corresponding assignments for the phosphines, sulfides, selenides, and phosphonium salts were based on both 1H and 13C NMR spectral data and the expected outcome of the reaction by literature precedent.For 1a, 1b and a series of derivatives, the 31P-13C coupling constants were found to be much larger than those observed in less rigid heterocyclic systems.They were consistent with previously reported Karplus relationships, provided a multiple-coupling path correction was made and coupling through nonbonded interactions was considered.Differences in the P-C coupling constants between the cis and trans isomers are also discussed.The 2J_PC coupling constants were dependent upon the geometry about phosphorus in the phosphines and in the oxides.Several reactions of the title compound and the salt derivatives are described.These include reaction of the dimethyl salt 13 with methyllithium to give norbornylene and trimethylphosphine as well as a ring-opened product 22.With the exception of the p-nitro-benzylphosphonium salt 12 which exhibited exocyclic P-C cleavage on treatment with aqueous NaOH, all of the salts led to ring opening.Treatment of both 1a and salt 13 with aqueous sodium deuteroxide gave ring opening with selective deuterium incorporation at the syn-C-7 position.